Low-k gate spacer and methods for forming the same

ABSTRACT

Embodiments of the present disclosure relate to a FinFET device having gate spacers with reduced capacitance and methods for forming the FinFET device. Particularly, the FinFET device according to the present disclosure includes gate spacers formed by two or more depositions. The gate spacers are formed by depositing first and second materials at different times of processing to reduce parasitic capacitance between gate structures and contacts introduced after epitaxy growth of source/drain regions.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/812,966, filed on Nov. 14, 2017, now U.S. Pat. No. 10,490,650, whichis hereby incorporated herein by reference.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed. When a semiconductor device such as a fin likefield-effect transistor (FinFET) is scaled down through varioustechnology nodes, several strategies have been employed to improvedevice performance, such as using epitaxy channels to enhance carriermobility.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion. The patent or application file contains at least one drawingexecuted in color. Copies of this patent or patent applicationpublication with color drawing(s) will be provided by the Office uponrequest and payment of the necessary fee.

FIG. 1 is an example of simplified Fin Field Effect Transistor (FinFET)devices in a three-dimensional view in accordance with some embodiments.

FIGS. 2A-C, 3A-C, 4A-C, 5A-C, 6A-C, 7A-C, 8A-C, 9A-C, 10A-C, 11A-C,12A-C, 13A-C, 14A-C, 15A-C, 16A-C, 17A-C, 18A-C, 19A-C, 20A-C, 21A-C,22A-C, 23A-C, 24A-C, 25A-C, 26A-C, 27A-C, and 28A-C are cross-sectionalviews of respective intermediate structures during intermediate stagesin an example process of forming a gate structure with gate spacers inFinFET devices in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments of the present disclosure relate to a FinFET device havinggate spacers with reduced capacitance and methods for forming the FinFETdevice. Particularly, the FinFET device according to the presentdisclosure includes gate spacers formed by two or more depositions. Thegate spacers are formed by depositing first and second materials atdifferent times of processing to reduce parasitic capacitance betweengate structures and contacts introduced after epitaxy growth ofsource/drain regions.

FIG. 1 schematically illustrates a device 100 in a three-dimensionalview. Other aspects not illustrated in or described with respect to FIG.1 may become apparent from the following figures and description. Thedevice 100 may be part of an IC, such as a microprocessor, memory cell,such as static random-access memory (SRAM), and/or other integratedcircuits. The device 100 may be electrically connected or coupled in amanner to operate as, for example, two transistors or more, such as fourtransistors.

The device 100 may include an N-type FinFET structure 102 and a P-typeFinFET structure 104. The N-type FinFET structure 102 includes fins 110a and 110 c on a P-doped region 106 a. The N-type FinFET structure 102includes isolation regions 108, and the fins 110 a and 110 c eachprotrude above and from between neighboring isolation regions 108. Gatestack 150 a is along sidewalls and over top surfaces of the fins 110 aand 110 c. The gate stack 150 a includes gate dielectric 158 a and gateelectrode 154 a over the gate dielectric 158 a. Source/drain regions 156a-b and 156 c-f are disposed in respective regions of the fins 110 a and110 c. Source/drain regions 156 a and 156 b are disposed in opposingregions of the fin 110 a with respect to the gate dielectric 158 a andgate electrode 154 a. Source/drain regions 156 e and 156 f are disposedin opposing regions of the fin 110 c with respect to the gate dielectric158 a and gate electrode 154 a.

In some examples, two transistors may be implemented in the N-typeFinFET structure 102 by: (1) source/drain regions 156 a and 156 b andthe gate stack 150 a; and (2) source/drain regions 156 e and 156 f andthe gate stack 150 a. Some source/drain regions may be shared betweenvarious transistors, for example. In some examples, various ones of thesource/drain regions may be connected or coupled together such that theN-type FinFET structure 102 is implemented as one functional transistor.For example, if neighboring (e.g., as opposed to opposing) source/drainregions 156 a, 156 e and 156 b, 156 f are electrically connected,respectively, such as through coalescing the regions by epitaxial growth(e.g., source/drain regions 156 a and 156 e being coalesced, andsource/drain regions 156 b and 156 f being coalesced), one functionaltransistor may be implemented. Other configurations in other examplesmay implement other numbers of functional transistors.

The P-type FinFET structure 104 includes fins 110 b and 110 d on aN-doped region 106 b. The P-type FinFET structure 104 includes isolationregions 108, and the fins 110 b and 110 d each protrude above and frombetween neighboring isolation regions 108. Gate stack 150 b is alongsidewalls and over top surfaces of the fins 110 b and 110 d. The gatestack 150 b includes gate dielectric 158 b and gate electrode 154 b overthe gate dielectric 158 b. Source/drain regions 156 c-d and 156 g-h aredisposed in respective regions of the fins 110 b and 110 d. Source/drainregions 156 c and 156 d are disposed in opposing regions of the fin 110b with respect to the gate dielectric 158 b and gate electrode 154 b.Source/drain regions 156 g and 156 h are disposed in opposing regions ofthe fin 110 d with respect to the gate dielectric 158 b and gateelectrode 154 b.

In some examples, two transistors may be implemented in the P-typeFinFET structure 104 by: (1) source/drain regions 156 c and 156 d andthe gate stack 150 b; and (2) source/drain regions 156 g and 156 h andthe gate stack 150 b. Some source/drain regions may be shared betweenvarious transistors, for example. In some examples, various ones of thesource/drain regions may be connected or coupled together such that theP-type FinFET structure 104 is implemented as one functional transistor.For example, if neighboring (e.g., as opposed to opposing) source/drainregions 156 c, 156 g and 156 d, 156 h are electrically connected,respectively, such as through coalescing the regions by epitaxial growth(e.g., source/drain regions 156 c and 156 g being coalesced, andsource/drain regions 156 d and 156 h being coalesced), one functionaltransistor may be implemented. Other configurations in other examplesmay implement other numbers of functional transistors.

FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section B-B is in a vertical plane along channelsin the fins 110 a, 110 b between opposing source/drain regions 156 a-d.Cross-section A-A is in a vertical plane perpendicular to cross-sectionB-B and is across the source/drain region 156 a in the fin 110 a andacross the source/drain region 156 e in the fin 110 c. Cross-section C-Cis in a vertical plane perpendicular to cross-section B-B and is acrossthe source/drain region 156 d in the fin 110 b and across thesource/drain region 156 h in the fin 110 d. Subsequent figures refer tothese reference cross-sections for clarity.

FIGS. 2A-C through 28A-C are cross-sectional views of respectiveintermediate structures during intermediate stages in an example processof forming a gate structure with gate spacers in, e.g., one or moreFinFETs, in accordance with some embodiments. In FIGS. 2A-C through28A-C, figures ending with an “A” designation illustrate cross-sectionalviews along a cross-section similar to cross-section A-A in FIG. 1;figures ending with a “B” designation illustrate cross-sectional viewsalong a cross-section similar to cross-section B-B in FIG. 1; andfigures ending with a “C” designation illustrate cross-sectional viewsalong a cross-section similar to cross-section C-C in FIG. 1. In somefigures, some reference numbers of components or features illustratedtherein may be omitted to avoid obscuring other components or features;this is for ease of depicting the figures.

FIGS. 2A, 2B, and 2C illustrate a semiconductor substrate 106 having afin mask 112 formed thereon for forming fins. The semiconductorsubstrate 106 may be or include a bulk semiconductor substrate, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Generally,an SOI substrate comprises a layer of a semiconductor material formed onan insulator layer. The insulator layer may be, for example, a buriedoxide (BOX) layer, a silicon oxide layer, or the like. The insulatorlayer is provided on a substrate, typically a silicon or glasssubstrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the semiconductor substrate may include silicon (Si);germanium (Ge); a compound semiconductor including silicon carbide,gallium arsenic, gallium phosphide, indium phosphide, indium arsenide,or indium antimonide; an alloy semiconductor including SiGe, GaAsP,AlInAs, AlGaAs, GaInAs, GaInP, or GaInAsP; or a combination thereof.

The semiconductor substrate 106 includes the P-doped region 106 a andN-doped region 106 b for forming N-type FinFET and P-type FinFETrespectively. One or both of the P-doped region 106 a and N-doped region106 b may be a doped well formed by implantation into the semiconductorsubstrate 106. For example, the semiconductor substrate 106 can be aP-type doped substrate, a part of which forms the P-doped region 106 a,and the N-doped region 106 b may be an N-doped well formed by implantingN-type dopants into the P-type doped substrate.

The fin mask 112 may be a hard mask used to form the fins 110 a-110 d.For example, one or more mask layers are deposited over thesemiconductor substrate 106 in the P-doped region 106 a and the N-dopedregion 106 b and then patterned into the fin mask 112. In some examples,the one or more mask layers may include or be silicon nitride, siliconoxynitride, silicon carbide, silicon carbon nitride, the like, or acombination thereof, and may be deposited by chemical vapor deposition(CVD), physical vapor deposition (PVD), atomic layer deposition (ALD),or another deposition technique. The one or more mask layers may bepatterned using photolithography. For example, a photo resist can beformed on the one or more mask layers, such as by using spin-on coating,and patterned by exposing the photo resist to light using an appropriatephotomask. Exposed or unexposed portions of the photo resist may then beremoved depending on whether a positive or negative resist is used. Thepattern of the photoresist may then be transferred to the one or moremask layers, such as by using a suitable etch process, which forms thefin mask. The etch process may include a reactive ion etch (RIE),neutral beam etch (NBE), the like, or a combination thereof. The etchingmay be anisotropic. Subsequently, the photo resist is removed in anashing process or wet strip process.

FIGS. 3A, 3B, and 3C illustrate that the semiconductor substrate 106 inthe P-doped region 106 a and the N-doped region 106 b is etched to formfins 110 a, 110 c, 110 b′, 110 d′ such that the fins 110 a, 110 c, 110b′, 110 d′ protrude from the P-doped region 106 a and the N-doped region106 b. The etch process may include a RIE, NBE, the like, or acombination thereof. The etching may be anisotropic.

As shown in FIGS. 4A, 4B, and 4C, after formation of the fins 110 a, 110b′, 110 c, 110 d′, an insulating material 107 may be deposited in thetrenches between the fins 110 a, 110 b′, 110 c, 110 d′. The insulatingmaterial 107 may be an oxide (such as silicon oxide), a nitride, thelike, or a combination thereof, and the insulating material may beformed by a high density plasma CVD (HDP-CVD), a flowable CVD (FCVD)(e.g., a CVD-based material deposition in a remote plasma system andpost curing to make it convert to another material, such as an oxide),the like, or a combination thereof. Other insulating materials formed byany acceptable process may be used. In the illustrated embodiment, theinsulating material 107 includes silicon oxide that is formed by a FCVDprocess. A planarization process, such as a chemical mechanical polish(CMP), may remove any excess insulating material and any remaining finmask to form top surfaces of the insulating material and top surfaces ofthe fins 110 a, 110 b′, 110 c, 110 d′ to be coplanar.

As shown in FIGS. 5A, 5B, and 5C, the fins 110 b′, 110 d′ may be etchedback after planarization of the insulating material 107. For example, amask 116 may be used to cover the P-doped region 106 a so that the fins110 b′, 110 d′ in the N-doped region 106 b may be etched formingrecesses 118 in the insulating material 107.

In FIGS. 6A, 6B, and 6C, replacement fins 110 b, 110 d are formed in therecesses 118 in the N-doped region 106 b by epitaxial growth. In someembodiments, the fins 110 b, 110 d may comprise silicon, silicongermanium (Si_(x)Ge_(1-x), where x can be between approximately 0 and100), silicon carbide, pure or substantially pure germanium, a III-Vcompound semiconductor, a II-VI compound semiconductor, or the like. Forexample, materials for forming a III-V compound semiconductor includeInAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like. In one embodiment, the replacement fins 110 b, 110 d includesilicon germanium to provide improved mobility for P-type FinFET.

In FIGS. 7A, 7B, and 7C, the insulating material 107 is recessed to formthe isolation regions 108. The insulating material 107 is recessed suchthat the fins 110 a, 110 b, 110 c, 110 d protrude from betweenneighboring isolation regions 108, which may, at least in part, therebydelineate the fins 110 a, 110 b, 110 c, 110 d as active areas in theP-doped region 106 a and N-doped region 106 b. The insulating material107 may be recessed using an acceptable etching process, such as onethat is selective to the material of the insulating material. Forexample, a chemical oxide removal using a CERTAS® etch or an AppliedMaterials SICONI® tool or dilute hydrofluoric (dHF) acid may be used.Further, top surfaces of the isolation regions 108 may have a flatsurface as illustrated, a convex surface, a concave surface (such asdishing), or a combination thereof, which may result from an etchprocess.

As shown in FIGS. 8A, 8B, and 8C after formation of the isolationregions 108, dummy gate stacks 120 a, 120 b are then formed on the fins110 a, 110 b, 110 c, 110 d. Each dummy gate stack 120 a, 120 b includesan interfacial dielectric 122, a dummy gate 124, an etch stop layer 125,and a hard mask 126. The interfacial dielectric 122, dummy gate 124,etch stop layer 125, and hard mask 126 may be formed by sequentiallydepositing respective layers and patterning those layers. For example, alayer for the interfacial dielectric 122 may include or be siliconoxide, silicon nitride, the like, or multilayers thereof, and may bethermally grown or deposited, such as by plasma-enhanced CVD (PECVD),ALD, or another deposition technique. A layer for the dummy gate 124 mayinclude or be silicon (e.g., polysilicon) or another material depositedby CVD, PVD, or another deposition technique. A layer for the hard mask126 may include or be silicon nitride, silicon oxynitride, siliconcarbon nitride, the like, or a combination thereof, deposited by CVD,PVD, ALD, or another deposition technique. The layers for the hard mask126, etch stop layer 125, dummy gate 124, and interfacial dielectric 122may then be patterned, for example, using photolithography and one ormore etch processes forming the dummy gate stacks 120 a, 120 b.

In FIGS. 9A, 9B, and 9C, a first spacer layer 128 is formed conformallyover the substrate 106. The first spacer layer 128 covers the topsurfaces and sidewalls of dummy gate stacks 120 a, 120 b, the topsurface of isolation regions 108, and the sidewalls and the top surfacesof the fins 110 a, 110 b, 110 c, 110 d. In some embodiments, the firstspacer layer 128 is made of silicon nitride (SiN), silicon oxycarbide(SiOC), silicon oxycarbonnitride (SiOCN), or other applicable dielectricmaterials. In some embodiments, the first spacer layer 128 includes oneor more low-k dielectric materials having a dielectric constant (k) lessthan 3.9. In one example, the first spacer layer 128 may have adielectric constant (k) in a range from about 3.9 to about 3.0. Thefirst spacer layer 128 may be formed by plasma enhanced CVD, lowpressure CVD, ALD, or other applicable processes.

In some embodiments, the thickness of the first spacer layer 128 is in arange from about 10 angstroms to about 30 angstroms. In someembodiments, the thickness of the first spacer layer 128 is in a rangefrom about 40% to about 60% of a designed thickness of gate spacers.

After the first spacer layer 128 is formed, a sacrificial layer 130 isformed over the first spacer layer 128 as shown in FIGS. 10A, 10B, and10C. The sacrificial layer 130 is configured to protect the first spacerlayer 128 from being damaged during subsequent processes, such as duringan epitaxial process to form epitaxial source/drain regions. Thesacrificial layer 130 may be a dielectric material that can standprocess conditions of an epitaxial deposition process and can beselectively etched away from the first spacer layer 128. For example,the sacrificial layer 130 may include one of silicon nitride, siliconcarbide nitride, silicon oxide, silicon oxynitride, or the like. In oneembodiment, the sacrificial layer 130 includes silicon nitride. Thesacrificial layer 130 may be formed by plasma enhanced CVD, low pressureCVD, ALD, or other applicable processes. The sacrificial layer 130 mayhave a thickness in a range from about 40 angstroms to about 60angstroms.

In FIGS. 11A, 11B, and 11C, a hard mask 132 is formed over the P-dopedregion 106 a to cover the N-type FinFET structure 102 while exposing theP-type FinFET structure 104 in the N-doped region 106 b. The hard mask132 may be formed through a photolithography process. In one embodiment,the hard mask 132 may be silicon nitride or the like.

In FIGS. 12A, 12B, and 12C, an etch process is performed to expose thefins 110 b, 110 d in the P-type FinFET structure 104 to formsource/drain regions therefrom. The etch process is an anisotropic etchprocess where the sacrificial layer 130 and the first spacer layer 128are etched along the z-direction while remaining substantially unchangedalong the x-direction and the y-direction (as shown in the coordinatesystem in FIG. 1). The anisotropic etch process may be performed by aRIE, NBE, or other suitable etch process.

As shown in FIG. 12B, the first spacer layer 128 and the sacrificiallayer 130 remain on the sidewalls of the dummy gate stack 120 b from upto a middle section of the hard mask 126. In one embodiment, the fins110 b, 110 d are recessed by a recess amount 110 r. The recess amount110 r may be in a range from about 0 nm to about 10 nm. The remainingfins 110 b, 110 d above the isolation region 108 are used to be a corefor the subsequent epitaxial process.

The sacrificial layer 130 protects the first spacer layer 128 fromlosing thickness during the etch process to expose the fins 110 b, 110d. With the first spacer layer 128 remaining over sidewalls of the dummygate 124, the dummy gate 124 may not suffer any side wall loss or damageduring the etch process. With the protection to the first spacer layer128 at the sidewalls of the dummy gate stack 120 b, the etch process maybe performed to completely remove the first spacer layer 128 from abottom portion of sidewalls 110 s of the fins 110 b, 110 d, thus,preventing poor epitaxial growth caused by the remaining first spacerlayer 128 during subsequent epitaxial process and preventing any cornerdamage caused by the remaining first spacer layer 128 on the sidewalls110 s of the fins 110 b, 110 d. The sacrificial layer 130 is over thehard mask 126 before the etch process and therefore is not exposed tothe etch process during at least a portion of the duration of the etchprocess, thus, allowing the dummy gate 124 to remain being covered thehard mask 126. With the dummy gate 124 being covered with no undesiredexposure, any undesirable epitaxial growth from the dummy gate 124, alsoknown as mushroom defects, may be prevented from occurring during thesubsequent epitaxial process. Additionally, the sacrificial layer 130may also prevent some loss of the isolation regions 108 during the etchprocess.

In FIGS. 13A, 13B, and 13C, an epitaxial process is performed to growepitaxial structures 134 b, 134 d from the fins 110 b, 110 d. Theepitaxial structures 134 b, 134 d are formed to function as source/drainregions for P-type FinFET devices. The epitaxial structures 134 b, 134 dmay include a single-element semiconductor material such as germanium(Ge) or silicon (Si); or compound semiconductor materials, such asgallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs); orsemiconductor alloy, such as silicon germanium (SiGe), gallium arsenidephosphide (GaAsP). In an embodiment, the epitaxial structures 134 b, 134d include an epitaxially grown silicon germanium (SiGe) to function assource/drain regions for P-type FinFET devices.

The epitaxial structures 134 b, 134 d are formed by a suitable epitaxialprocess, for example, a selective epitaxial growth (SEG) process, achemical vapor deposition (CVD) process (e.g., vapor-phase epitaxy(VPE), a low pressure chemical vapor deposition (LPCVD), and/orultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy (MBE), liquidphase epitaxy (LPE), or combinations thereof. The formation process ofthe epitaxial structures 134 b, 134 d may use gaseous and/or liquidprecursors, which may interact with the composition of the fins 110 b,110 d thereunder.

The epitaxial structures 134 b, 134 d may be doped or undoped in-situduring the epitaxial process. For example, the epitaxially grown SiGeepitaxial structure may be doped with boron. The doping may be achievedby an ion implantation process, plasma immersion ion implantation (PIII)process, gas and/or solid source diffusion process, another suitableprocess or combinations thereof. The epitaxial structures 134 b, 134 dmay further be exposed to an annealing process, such as a rapid thermalannealing (RTA) and/or laser annealing process. The annealing processmay be used to activate the dopants. If the epitaxial structures 134 b,134 d are not doped in-situ, a second implantation process (e.g., ajunction implant process) is performed to dope the epitaxial structures134 b, 134 d.

The epitaxial structures 134 b, 134 d are strained and stressed toenhance carrier mobility of the FinFET device structure and enhance theFinFET device structure performance. The performance of the P-typeFinFET structure 104 may be relative to the volume of the epitaxialstructures 134 b, 134 d. For example, if the volume of the epitaxialstructures 134 b, 134 d is increased, the operation speed of the P-typeFinFET structure 104 is also increased. In FIG. 13C, the cross sectionalshape of each epitaxial structures 134 b, 134 d is substantially arhombus shape as a result that silicon germanium is formed moreefficiently along its crystal planes. However, the shape of theepitaxial structures 134 b, 134 d is not intended to be limiting.

In FIGS. 14A, 14B, and 14C, the hard mask 132 and the sacrificial layer130 are removed by an etch process. In one embodiment, the hard mask 132and the sacrificial layer 130 may be removed by a wet etching process.For example, the hard mask 132 and the sacrificial layer 130 are removedusing a wet etchant comprising H₃PO₄. Other suitable etchants, such asHF or the like may also be used.

As shown in FIGS. 15A, 15B, and 15C, after the hard mask 132 and thesacrificial layer 130 are removed, a sacrificial layer 136 may be formedover the substrate 106 over both the P-doped region 106 a and theN-doped region 106 b. The sacrificial layer 136 is configured to protectthe first spacer layer 128 during the subsequent fin recess process andepitaxial process in the P-doped region 106 a. The sacrificial layer 136is similar to the sacrificial layer 130. The sacrificial layer 136 maybe a dielectric material that can stand process conditions of anepitaxial deposition process and can be selectively etched away from thefirst spacer layer 128. For example, the sacrificial layer 136 mayinclude one of silicon nitride, silicon carbide nitride, silicon oxide,silicon oxynitride, or the like. In one embodiment, the sacrificiallayer 136 includes silicon nitride. The sacrificial layer 136 may beformed by plasma enhanced CVD, low pressure CVD, ALD, or otherapplicable processes. The sacrificial layer 136 may have a thickness ina range from about 40 angstroms to about 60 angstroms.

In FIGS. 16A, 16B, and 16C, a hard mask 138 is formed over the N-dopedregion 106 b to cover the P-type FinFET structure 104 while exposing theN-type FinFET structure 102 in the P-doped region 106 a. The hard mask138 may be formed through a photolithography process. In one embodiment,the hard mask 138 may be silicon nitride or the like.

In FIGS. 17A, 17B, and 17C, an etch process is performed to recess thefins 110 a, 110 c in the N-type FinFET structure 102 so that epitaxialsource/drain regions can be formed. The etch process is an anisotropicetch process where the sacrificial layer 136 and the first spacer layer128 are etched along the z-direction while remaining substantiallyunchanged along the x-direction and the y-direction. The anisotropicetch process may be performed by a RIE, NBE, or other suitable etchprocess.

As shown in FIG. 17B, the first spacer layer 128 and the sacrificiallayer 136 remain on the sidewalls of the dummy gate stack 120 a from upto a middle section of the hard mask 126. As shown in FIG. 17A, afterthe etch process, a spacer portion 128 r of the first spacer layer 128remains over a top surface 108 s of the isolation regions 108. A height142 of the spacer portion 128 r may be in a range from about 0 nm toabout 10 nm. Recesses 140 are formed between the spacer portions 128 r.The recesses 140 may be used to limit horizontal growth during theinitial stage of growing epitaxial source/drain regions.

The sacrificial layer 136 protects the first spacer layer 128 fromlosing thickness during recessing the fins 110 a, 110 c. With the firstspacer layer 128 remaining over sidewalls of the dummy gate 124, thedummy gate 124 in the dummy gate stack 120 a may not suffer any sidewall loss or damage during the etch process. With the protection to thefirst spacer layer 128 at the sidewalls of the dummy gate stack 120 a,the etch process may be performed to control the height 142 of thespacer portion 128 r, thus, achieving suitable height 142 to thedimension of the epitaxial source/drain regions to be grown in thesubsequent epitaxial process. With suitable height of the spacer portion128 r, merging or coalescing of epitaxial source/drain regions betweenneighboring fins are prevented, thus, improving CD control. Thesacrificial layer 136 is over the hard mask 126 before the etch processand therefore is not exposed to the etch process during at least aportion of the duration of the etch process, thus, allowing the dummygate 124 to remain being covered the hard mask 126. With the dummy gate124 being covered with no undesired exposure, any undesirable epitaxialgrowth from the dummy gate 124, also known as mushroom defects, may beprevented from occurring during the subsequent epitaxial process.Additionally, the sacrificial layer 136 may also prevent loss of theisolation regions 108 during the etch process.

In FIGS. 18A, 18B, and 18C, an epitaxial process is performed to growepitaxial structures 134 a, 134 c from the fins 110 a, 110 c in therecesses 140. The epitaxial structures 134 a, 134 c are formed tofunction as source/drain regions for N-type FinFET devices. Theepitaxial structures 134 a, 134 c may be silicon including N-typedopants, such as phosphorus, carbon, or combinations thereof.

The epitaxial structures 134 a, 134 c are formed by a suitable epitaxialprocess, for example, a selective epitaxial growth (SEG) process, achemical vapor deposition (CVD) process (e.g., vapor-phase epitaxy(VPE), a low pressure chemical vapor deposition (LPCVD), and/orultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy (MBE), liquidphase epitaxy (LPE), or combinations thereof. The formation process ofthe epitaxial structures 134 a, 134 c may use gaseous and/or liquidprecursors, which may interact with the composition of the fins 110 a,110 c thereunder.

The epitaxial structures 134 b, 134 d may be doped or undoped in-situduring the epitaxial process. For example, the epitaxially grown Siepitaxial structure may be doped with carbon to form a Si:C epitaxialstructure, phosphorous to form a Si:P epitaxial structure, or bothcarbon and phosphorous to form a SiCP epitaxial structure. The dopingmay be achieved by an ion implantation process, plasma immersion ionimplantation (PIII) process, gas and/or solid source diffusion process,another suitable process, or combinations thereof. The epitaxialstructures 134 a, 134 c may further be exposed to an annealing process,such as a rapid thermal annealing (RTA) process and/or laser annealingprocess. The annealing process may be used to activate the dopants. Ifthe epitaxial structures 134 a, 134 c are not doped in-situ, a secondimplantation process (e.g., a junction implant process) is performed todope the epitaxial structures 134 a, 134 c.

The epitaxial structures 134 a, 134 c are strained and stressed toenhance carrier mobility of the FinFET device structure and enhance theFinFET structure performance. As shown in FIG. 18A, epitaxial structures134 a, 134 c are first grown vertically in the recesses 140, duringwhich time the epitaxial structure 134 a, 134 b do not growhorizontally. After the recesses 140 are fully filled, the epitaxialstructures 134 a, 134 b may grow both vertically and horizontally toform facets corresponding to crystalline planes of the substrate 106. InFIG. 18A, the cross sectional shape of each epitaxial structures 134 a,134 c is substantially a rhombus shape as a result that silicon carbon,silicon phosphorous, or silicon carbon phosphorous is formed moreefficiently along its crystal planes. However, the shape of theepitaxial structures 134 a, 134 c is not intended to be limiting.

In FIGS. 19A, 19B, and 19C, the hard mask 138 and the sacrificial layer136 are removed by an etch process. In one embodiment, the hard mask 138and the sacrificial layer 136 may be removed by a wet etching process.For example, the hard mask 138 and the sacrificial layer 136 are removedusing a wet etchant comprising H₃PO₄. Other suitable etchants, such asHF or the like may also be used.

In FIGS. 20A, 20B, and 20C, a second spacer layer 144 is conformallyformed over the substrate 106. The second spacer layer 144 covers thetop surface and sidewalls of dummy gate stacks 120 a, 120 b, the topsurface of isolation regions 108, and the sidewalls and the top surfaceof the epitaxial structures 134 a, 134 b, 134 c, 134 d. In someembodiments, the second spacer layer 144 is or includes siliconoxycarbide (SiOC), silicon oxycarbonnitride (SiOCN), or other applicabledielectric materials.

In some embodiments, the second spacer layer 144 includes one or morelow-k dielectric materials having a dielectric constant (k) equal to orless than 3.9. In one example, the second spacer layer 144 may includelow-k dielectric materials having a dielectric constant (k) in a rangefrom about 3.9 to about 2.5. The second spacer layer 144 may be formedby plasma enhanced CVD, low pressure CVD, ALD, or other applicableprocesses. In some embodiment, the second spacer layer 144 is a porousdielectric film. The second spacer layer 144 may include pores having amedian radius in a range from about 0.4 nm to about 0.43 nm. The secondspacer layer 144 may have a porosity in a range between about 2.00% toabout 3.50%. For example, the second spacer layer 144 may have aporosity of about 3.27%.

In some embodiments, the thickness of the second spacer layer 144 is ina range from about 20 angstroms to about 40 angstroms. In someembodiments, the thickness of the second spacer layer 144 is in a rangefrom about 40% to about 70% of a designed thickness of gate spacers. Inone embodiment, the second spacer layer 144 has a conformity in a rangebetween about 90% to about 100%.

In FIGS. 21A, 21B, and 21C, a contact etch stop layer (CESL) 146 isconformally formed over substrate 106 to cover the second spacer layer144. In some embodiments, the contact etch stop layer 146 is made ofsilicon nitride, silicon oxynitride, and/or other applicable materials.The contact etch stop layer 146 may be formed by plasma enhanced CVD,low pressure CVD, ALD, or other applicable processes.

In FIGS. 22A, 22B, and 22C, an inter-layer dielectric (ILD) layer 148 isformed over the contact etch stop layer 146 over substrate 106 inaccordance with some embodiments. The inter-layer dielectric layer 148may include one or multiple layer including dielectric materials, suchas silicon oxide, silicon nitride, silicon oxynitride, tetraethoxysilane(TEOS), phosphosilicate glass (PSG), borophosphosilicate glass (BPSG),low-k dielectric material, and/or other applicable dielectric materials.Examples of low-k dielectric materials include, but are not limited to,fluorinated silica glass (FSG), carbon doped silicon oxide, amorphousfluorinated carbon, parylene, bis-benzocyclobutenes (BCB), or polyimide.The inter-layer dielectric layer 148 may be formed by chemical vapordeposition (CVD), physical vapor deposition, (PVD), atomic layerdeposition (ALD), spin-on coating, or other applicable processes.

After forming the inter-layer dielectric layer 148, a planarizationprocess is performed to expose the top surface of the dummy gates 124 asshown in FIGS. 23A, 23B, and 23C. In some embodiments, the planarizationprocess may be a chemical mechanical polishing (CMP) process.

After the planarization process, the dummy gates 124 are removed to formtrenches 160, as shown in FIGS. 24A, 24B, and 24C. The dummy gates 124may be removed by performing a first etching process and performing asecond etching process after the first etching process.

In some embodiments, the first etching process is a dry etching processand the second etching process is a wet etching process. In someembodiments, the dry etching process includes using an etching gas suchas CF₄, Ar, NF₃, Cl₂, He, HBr, O₂, N₂, CH₃F, CH₄, CH₂F₂, or acombination thereof. In some embodiments, the dry etching process isperformed at a temperature in a range from about 20° C. to about 80° C.In some embodiments, the dry etching process is performed at a pressurein a range from about 1 mtorr to about 100 mtorr. In some embodiments,the dry etching process is performed at a power in a range from about 50W to about 1500 W. The wet etching process may include using HF andNH₄OH. In some embodiments, wet etching process is performed at atemperature in a range from about 30° C. to about 200° C. In someembodiments, wet etching process is performed for a time in a range fromabout 20 seconds to about 400 seconds.

After the dummy gates 124 are removed, replacement gate stacks 150 a,150 b are formed in the trenches 160. As shown in FIGS. 25A, 25B, and25C, a high-k dielectric layer 162 a, 162 b for the N-type FinFETstructure 102 and P-type FinFET structure 104 is deposited. In someembodiments, the high-k dielectric layer 162 a, 162 b is or includesmetal oxides, metal nitrides, metal silicates, transition metal-oxides,transition metal-nitrides, transition metal-silicates, or oxynitrides ofmetals. Examples of the high-k dielectric material include, but are notlimited to, hafnium oxide (HfO₂), hafnium silicon oxide (HfSiO), hafniumsilicon oxynitride (HfSiON), hafnium tantalum oxide (HfTaO), hafniumtitanium oxide (HfTiO), hafnium zirconium oxide (HfZrO), siliconnitride, silicon oxynitride, zirconium oxide, titanium oxide, aluminumoxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, or other applicabledielectric materials.

In some embodiments, the high-k dielectric layer 162 a, 162 b may beformed from different materials for the N-type FinFET structure 102 andP-type FinFET structure 104. Patterned masks may be used to form thehigh-k dielectric layer 162 a, 162 b separately.

As shown in FIGS. 26A, 26B, and 26C, work function tuning layers 164 a,164 b are formed over high-k dielectric layer 162 a, 162 b. The workfunction tuning layer 164 a, 164 b may be implemented to tune a workfunction. In some embodiments, the work function tuning layers 164 a,164 b may be formed from different materials for the N-type FinFETstructure 102 and P-type FinFET structure 104. Patterned masks may beused to form the work function tuning layers 164 a, 164 b separately.

The work function tuning layer 164 a may include N-type work functionmaterials for the N-type FinFET structure 102. Examples of N-type workfunction materials include, but are not limited to, titanium aluminide(TiAl), titanium aluminum nitride (TiAlN), carbo-nitride tantalum(TaCN), hafnium (Hf), zirconium (Zr), titanium (Ti), tantalum (Ta),aluminum (Al), metal carbides (e.g., hafnium carbide (HfC), zirconiumcarbide (ZrC), titanium carbide (TiC), aluminum carbide (AlC)),aluminides, and/or other applicable materials.

The work function tuning layer 164 b may include P-type work functionmaterials for the P-type FinFET structure 104. Examples of P-type workfunction materials include, but are not limited to, titanium nitride(TiN), tungsten nitride (WN), tungsten (W), ruthenium (Ru), palladium(Pd), platinum (Pt), cobalt (Co), nickel (Ni), conductive metal oxides,and/or other applicable materials.

In FIGS. 27A, 27B, and 27C, a metal gate electrode layer 166 is formedover work function tuning layer 164 a, 164 b. In some embodiments, metalgate electrode layer 166 is made of a conductive material, such asaluminum, copper, tungsten, titanium, tantalum, titanium nitride,tantalum nitride, nickel silicide, cobalt silicide, TaC, TaSiN, TaCN,TiAl, TiAlN, or other applicable materials. The metal gate electrodelayer 166 may be formed by CVD, ALD, PVD, metal-organic chemical vapordeposition (MOCVD), plating, and/or other suitable processes.

In FIGS. 28A, 28B, and 28C, a planarization process, such as a CMPprocess, is performed after formation of the metal gate electrode layer166 until the first spacer layer 128 and the second spacer layer 144 areexposed. As shown in FIG. 28B, the first spacer layer 128 coverssidewalls of the high-k dielectric layer 162 a, 162 b of the gate stacks150 a, 150 b and a portion of top surface, sidewalls of the fins 110 a,110 c, 110 b, 110 d at both ends of the channel region. The secondspacer layer 144 covers the first spacer layer 128 at the sidewalls ofthe gate stacks 150 a, 150 b, top surfaces and sidewalls of thesource/drain regions 134 a, 134 b, 134 c, 134 d, and top surfaces of theisolation regions 108.

Embodiments of the present disclosure provide a method of forming gatespacers by depositing a first spacer layer and a sacrificial layer priorto fin recessing, and depositing a second spacer layer after epitaxialgrowth. The methods may be used to form epitaxial source/drain regionsfor P-type FinFET structures or N-type FinFET structures. The method mayprevent thickness loss of the gate spacers, may avoid sidewall loss indummy gates, prevent corner damage in the gate structure, avoid mushroomdefects, and prevent loss of the isolation regions.

One embodiment of the present disclosure provides method includingforming a first dielectric layer over a fin structure and a dummy gatestack, the dummy gate stack being over the fin structure; conformallydepositing a sacrificial layer over the first dielectric layer;performing an anisotropic etch process to expose portions of the finstructure while sidewalls of the dummy gate stack remain covered by thesacrificial layer and the first dielectric layer; growing source/drainregions from the exposed portions of the fin structure; removing thesacrificial layer to expose the first dielectric layer; and depositing asecond dielectric layer on the first dielectric layer.

Another embodiment of the present disclosure provides a structureincluding a fin structure having source/drain regions on a substrate; ametal gate structure between the source/drain regions on the finstructure, wherein the metal gate structure includes a conformal high-kdielectric layer over the fin structure; and a gate electrode over theconformal high-k dielectric layer; a first gate spacer along a sidewallof the metal gate structure; and a second gate spacer along the firstgate spacer and over the source/drain regions of the fin structure,wherein the first gate spacer is disposed between the metal gatestructure and the second gate spacer.

Yet another embodiment of the present disclosure provides a method,including forming a dummy gate stack over a fin structure, forming afirst spacer layer over the fin structure and the dummy gate stack,depositing a sacrificial layer over the first spacer layer, recessingthe fin structure on both sides of the dummy gate stack, growingsource/drain regions from the recessed fin structure, removing thesacrificial layer to expose the first spacer layer; and depositing asecond spacer layer over the first spacer layer, the source/drainregion, and the dummy gate stack; depositing a contact etch stop layerover the second spacer layer; removing the dummy gate stack to form arecess between remaining portions of the first spacer layer; and forminga metal gate stack in the recess.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of forming a semiconductor device, themethod comprising: forming a first dummy gate over a first fin structureand a second dummy gate over a second fin structure; forming a firstspacer layer over the first dummy gate, the first fin structure, thesecond dummy gate, and the second fin structure; forming a firstsacrificial layer over the first spacer layer; removing portions of thefirst sacrificial layer and the first spacer layer to expose the firstfin structure; forming first source/drain regions on the first finstructure; removing the first sacrificial layer; forming a secondsacrificial layer over the first spacer layer, the first dummy gate, thefirst source/drain regions, the second dummy gate, and the second finstructure; removing portions of the second sacrificial layer and thefirst spacer layer to expose the second fin structure, wherein, afterremoving portions of the second sacrificial layer and the first spacerlayer to expose the second fin structure, portions of the first spacerlayer remain along sidewalls of the second fin structure to form spacerportions; forming second source/drain regions on the second finstructure; and forming a second spacer layer over remaining portions ofthe first spacer layer.
 2. The method of claim 1, wherein forming thesecond source/drain regions comprises: recessing the second finstructure between the spacer portions; and epitaxially growing anepitaxial layer, the epitaxial layer protruding above the spacerportions.
 3. The method of claim 1, wherein sidewalls of the first finstructure in source/drain regions are free of the first spacer layerwhile forming the first source/drain regions.
 4. The method of claim 1,a thickness of the first spacer layer is in a range from about 40% toabout 60% of a combined thickness of the first spacer layer and thesecond spacer layer.
 5. The method of claim 1, wherein the firstsacrificial layer comprises silicon nitride, silicon carbide nitride,silicon oxide, or silicon oxynitride.
 6. A method of forming asemiconductor device, the method comprising: forming a first finstructure in a first substrate region; forming a second fin structure ina second substrate region; forming a first dummy gate stack over thefirst fin structure; forming a second dummy gate stack over the secondfin structure; forming a first gate spacer layer over the first finstructure, the first dummy gate stack, the second fin structure, and thesecond dummy gate stack; forming a first sacrificial layer over thefirst gate spacer layer in the first substrate region and the secondsubstrate region; forming a first mask over the first sacrificial layerin the second substrate region; performing a first etch process toremove portions of the first sacrificial layer and the first gate spacerlayer and to expose portions of the first fin structure, wherein afterperforming the first etch process remaining portions of the first gatespacer layer adjacent the first dummy gate stack form a first gatespacer, wherein after performing the first etch process portions ofsidewalls of the first dummy gate stack remain covered by the firstsacrificial layer and the first gate spacer; growing first source/drainregion on the first fin structure; removing the first mask; removingremaining portions of the first sacrificial layer; forming a secondsacrificial layer over the first gate spacer layer in the secondsubstrate region and over the first gate spacer in the first substrateregion; forming a second mask over the second sacrificial layer in thefirst substrate region; performing a second etch process to removeportions of the second sacrificial layer and the first gate spacer layerin the second substrate region, wherein after performing the second etchprocess remaining portions of the first gate spacer layer adjacent thesecond dummy gate stack form a second gate spacer, remaining portions ofthe first gate spacer layer adjacent the second fin structure formspacer portions on opposing sides of the second fin structure, whereinafter performing the second etch process portions of sidewalls of thesecond dummy gate stack remain covered by the second sacrificial layerand the second gate spacer; growing second source/drain region on thesecond fin structure, wherein the second source/drain region is adjacentthe second gate spacer; removing remaining portions of the secondsacrificial layer; and forming a second gate spacer layer over the firstgate spacer in the first substrate region and over the second gatespacer layer in the second substrate region.
 7. The method of claim 6,wherein the second source/drain region extends between the spacerportions.
 8. The method of claim 6 further comprising: prior to growingthe first source/drain region, recessing the first fin structure; andprior to growing the second source/drain region, recessing the secondfin structure.
 9. The method of claim 8, wherein recessing the secondfin structure comprises recessing the second fin structure below anupper surface of the spacer portions.
 10. The method of claim 6, whereinthe second gate spacer layer extends over the first source/drain regionand the second source/drain region.
 11. The method of claim 10, whereinthe second gate spacer layer directly contacts the spacer portions inthe second substrate region.
 12. A semiconductor device comprising: afirst transistor on a substrate, the first transistor comprising: afirst epitaxial source/drain region over a first fin; a first metal gatestructure adjacent the first epitaxial source/drain region, wherein thefirst metal gate structure includes: a first high-k dielectric layerover the first fin; and a first gate electrode over the first high-kdielectric layer; a first gate spacer along a sidewall of the firstmetal gate structure; and a second gate spacer along a sidewall of thefirst gate spacer and over the first epitaxial source/drain region,wherein the first gate spacer is disposed between the first metal gatestructure and the second gate spacer, wherein a thickness of the secondgate spacer is 40% to 70 % of a total thickness of the first gate spacerand the second gate spacer; and a second transistor on the substrate,the second transistor comprising: a second epitaxial source/drain regionover a second fin, the second epitaxial source/drain region having asmaller cross-sectional area than the first epitaxial source/drainregion; a second metal gate structure adjacent the second epitaxialsource/drain region, wherein the second metal gate structure includes: asecond high-k dielectric layer over the second fin; and a second gateelectrode over the second high-k dielectric layer; a third gate spaceralong a sidewall of the second metal gate structure; a fourth gatespacer along a sidewall of the second gate spacer and over the secondepitaxial source/drain region, wherein the third gate spacer is disposedbetween the second metal gate structure and the fourth gate spacer; andspacer portions along opposing sidewalls of the second epitaxialsource/drain region.
 13. The semiconductor device of claim 12 furthercomprising an etch stop layer over the second gate spacer.
 14. Thesemiconductor device of claim 12, wherein the first gate spacer and thethird gate spacer have a thickness in a range from 10 angstroms to 30angstroms.
 15. The semiconductor device of claim 12, wherein the secondgate spacer and the fourth gate spacer has a thickness in a range from20 angstroms to 40 angstroms.
 16. The semiconductor device of claim 12,wherein the second gate spacer includes pores having a median radius ina range from about 0.4 nm to about 0.43 nm.
 17. The semiconductor deviceof claim 12, wherein the second gate spacer is a porous film having aporosity in a range from 2.00% to 3.50%.
 18. The semiconductor device ofclaim 12, wherein a height of the spacer portions is in a range fromabout 0 nm to about 10 nm.
 19. The semiconductor device of claim 12,wherein the second gate spacer covers an upper surface of the firstepitaxial source/drain region.
 20. The method of claim 1, wherein thesecond spacer layer extends over an upper surface of the firstsource/drain regions and the second source/drain regions.